Historical research guide · 1128 · 1935
Note on the Transmutation Function for Deuterons
J. R. Oppenheimer · M. Phillips
In one minute
Two pages in 1935 explained a puzzle in early accelerator data, and the mechanism they named is still one of the two textbook routes chapter 12 needs. Fire a deuteron at a nucleus and, on the simplest picture, the Coulomb barrier should hold it off exactly as it holds off a proton or an alpha particle, so the reaction rate should climb steeply with the deuteron's energy. It does not. Oppenheimer and Phillips point to what makes a deuteron different from a bare charge: it is a loosely bound pair, large for its mass and easily polarized, so as it approaches a nucleus it can be stretched, presenting its neutron to the target while its proton is still held at a distance. The neutron is captured while the proton is repelled away. Because it is the neutron that has to arrive, the Coulomb repulsion is less effective than it is for a proton or an alpha, and the resulting transmutation function rises more slowly with energy. They treat the collision in the adiabatic approximation and report the energy dependence as being in good agreement with experiment.
Connection
Chapter 12 rests on two pieces of settled nuclear physics — electron screening and this stripping reaction — being enough to explain what the NASA Glenn deuterated-metal experiments report, without anything exotic being invoked. This is the original statement of the second of those two, and it is the reason a deuteron in a lattice can react at energies a bare proton could not.
From the source
The starting point is a property of the deuteron rather than of the target: the finite size and ready polarizability of the deuteron change the probability of transmutations involving the capture of the neutron.Abstract, first sentence
The consequence is that the Coulomb repulsion of the nucleus is less effective than it is for alpha particles or protons — the barrier still exists, but a polarized deuteron does not meet it the way a bare charge of the same energy does.Abstract, second sentence
Therefore the corresponding transmutation functions increase less rapidly with deuteron energy than the functions for protons or alpha particles do — which is the measurable signature of the process and the anomaly the paper was written to explain.Abstract, second sentence
The calculation treats the collision by the adiabatic approximation, on the reasoning that the deuteron's internal motion is slow compared with the approach, so the pair has time to stretch as the field of the nucleus rises.Abstract, third sentence
The result was checked against data at the time, not merely proposed: the authors obtain quantitative results for the energy dependence which they state are in good agreement with experiment.Abstract, closing sentence
The way in
https://doi.org/10.1103/PhysRev.48.500How to cite it
J. R. Oppenheimer, M. Phillips (1935) Note on the Transmutation Function for Deuterons doi:10.1103/PhysRev.48.500